Eutrophication control in the Netherlands

Due to the limited perspectives of the Dutch national policy and due to the unique conditions and constraints of individual lake systems, tailor-made programs are needed for the restoration of freshwater lakes. Based on an ev aluation of several restoration projects, a guideline is provided to enable water managers to develop such a restoration program. This guide-line is s ummarized in the paper and important topics, such as the definition of targ ets and standards, system identification and measures, are highlighted. Tar gets should include a natural reference, but also the constraints imposed b y other functions of the lake. Monitoring and system identification are nec essary to determine the extent of remedial measures and whether they should focus on external nutrient sources, internal sources or other factors, suc h as the food web structure. It is advocated that for lakes which have not degraded to a green, algal-dominated, turbid state, prevention or re-establ ishment of its ability to self-restore are preferred to 'intensive surgery' on the system. Lake re-creation can be applied if the system is heavily pe rturbed. In that case the re-creation of a more beneficial system is a more fair-minded approach than restoration of the natural state.